Self-generated gas blast circuit interrupter embodying high molecular weight polyoxymethylenes



G. C. GAINER ETAL Oct. 16, 1962 3,059,081 SELF-GENERATED GAS BLASTCIRCUIT INTERRUPTER EMBODYING HIGH MOLECULAR WEIGHT POLYOXYMETHYLENESFiled Sept. 4, 1959 Fig. l.

2 Sheets-Sheet l Fig.2.

Fig.3.

Boric Acid 5 Half Cycles I II I I Polyoxymethylene at 5 Half Cycles.

ll'lllll lllllll R. M..S. Ampere:

Oct. 16, 1962 G c. GAINER ETAL 3,059,081

SELF-GENERATED GAS BLAST CIRCUIT INTERRUPTER EMBODYING HIGH MOLECULARWEIGHT POLYOXYMETHYLENES Filed Sept. 4, 1959 2 Sheets-Sheet 2 Fig.4.

IIIIIIIII IIIIIIIIIIIIIIIIIII United States Patent SELF-GENERATED GASBLAST CIRCUIT IN- TERRUPTER EMBODYING HIGH MOLECULAR WEIGHTPOLYOXYMETHYLENES Gordon C. Gainer, Penn l-IiHs, and Albert P. Strom,Forest Hills, Pa., assignors to Westinghouse Electric Corporation, EastPittsburgh, Pa., a corporation of Pennsylvania Filed Sept. 4, 1959, Ser.No. 838,332 Claims. (Cl. 200-149) The present invention relates tocircuit interrupters which generate arc-extinguishing and confininggases automatically upon the occurence of an arc, and has particularreference to electrical devices embodying high molecular weightpolyoxymethylenes as an arc confining and extinguishin g member.

Heretofore, a relatively large number of arc confining and extinguishingmaterials have been suggested for use in circuit interrupters. Certainprior art materials have proven to be so outstanding in this respectthat they often are selected as a standard of comparison of materials.Specifically, horn or vulcanized fiber and compressed boric acid havebeen accepted as standards of comparison because each of these materialshas exhibited generally desirable characteristics over a wide range ofconditions of use.

The surprising discovery now has been made that high molecular Weightpolyoxymethylenes provide unusually good characteristics as gasgenerating materials when exposed to arcs. It has been found, over awide range of current, that such polyoxymethylenes are in many casessuperior in the restored voltage to horn fiber. For certainapplications, polyoxymethylenes have given results such that it ispossible to use these materials in applications where boric acid cannotbe used. Consequently, high molecular weight polyoxymethylenes possesscertain unexpectedly superior characteristics to the best materials,indeed the standard materials, available to the art at the present timefor use as an arc-extinguishing medium.

The object of this invention is to provide in a circuit interrupter anarc confining and interrupting structure comprising high molecularweight polyoxymethylenes.

Another object of the invention is to embody in a self-generated gasblast circuit interrupter an arc confining and interrupting structurecomprising a body composed of at least 70% by weight of high molecularweight polyoxymethylenes.

Other objects of the invention will, in part, be obvious, and will, inpart, appear hereinafter.

For a more complete understanding of the present invention reference ismade to the following description taken in conjunction with theaccompanying drawing, in which:

FIGURE 1 is a vertical cross-section view through a fuse;

FIG. 2 is a view in elevation, partly in section, of a self-expulsiontype of lightning arrester;

FIG. 3 is a graph plotting restored kilovolts against amperage for fibreand high molecular weight polyoxymethylenes and boric acid; and

FIG. 4 is a side elevational view, partially in section, of an oil-typecircuit interrupter embodying molded grids in accordance with theinvention.

In accordance with the present invention and in the attainment of theforegoing objects, arc-confining and arc-extinguishing gas generatorportions of circuit interrupters are prepared from formaldehydepolymers, specifically, high molecular weight polyoxymethylenes. Theformaldehyde polymers of this invention are obtained by continuouslypassing gaseous, substantially anhydrous, monomeric formaldehyde into areaction zone containing a reaction medium which is inert toformaldehyde, under the conditions of reaction, and permitting theformaldehyde to polymerize continuously as the monomer is introducedtherein.

The high molecular weight polyoxymcthylenes of this invention aredisclosed fully in US. Patent No. 2,768,994. The disclosure contained inthat patent is incorporated herein by reference. These polymers aredefined as either having a minimum of toughness retention, defined as adegree of toughness of at least 1, or having a minimum thermalstability, defined as a reaction rate constant for thermal degradationat 222 C. of less than 1% by weight of the polymer per minute.

As disclosed in US. Patent No. 2,768,994, these polyoxymethylenes may beprepared in several Ways. One satisfactory process for preparing thehigh molecular weight polyoxymethylenes consists of passing a continuousstream, consisting essentially of monomeric formaldehyde in aconcentration of at least 99.5% formaldehyde, into contact with a twocomponent polymerization reaction medium. Said medium consists of (1), aliquid hydrocarbon having from 3 to 10 carbon atoms per molecule. Thehydrocarbon may be selected from the group consisting of aliphatichydrocarbons, cycloaliphatic hydrocarbons, and aromatic hydrocarbons.The second ingredient of the polymerization reaction medium is (2) acatalytic amount of a compound selected from the group consisting ofprimary, secondary, and tertiary aliphatic amines; primary, secondary,and tertiary cycloaliphatic amines; and primary aromatic amines. Theresultant mixture of formaldehyde and polymerization reaction medium iscontinuously agitated at a temperature within the range of from about 50C. to about +70 C. at substantially atmospheric pressure. The polymericparticles formed comprise high molecular weight polyoxymethylene.

The high molecular weight polyoxymethylenes are thermoplastic in natureand, therefore, will melt when heated to substantially hightemperatures. In cases where melting and softening is found to beundesirable, thermosetting resins may be incorporated with the highmolecular polyoxymethylene in amounts up to about 30% by weight.Examples of suitable thermosetting resins which may be so incorporatedinclude polyester resins, epoxy resins, silicone resins, and the like.The high molecular weight polyoxymethylene polymers, either alone or incombination with the thermosetting resins, may be molded conveniently orextruded in the form of tubes, bars, tapes, and the like. It isparticularly convenient, for example, to extrude the polymer in the formof tubes of one-quarter to one-half inch internal diameter, such tubesthen only need to be cut or sawed to length whereby they are ready foruse in fuse manufacture. The finished molded polymer may be readilymachined to any predetermined shape.

The high molecular weight polyoxymethylene polymers of this inventionare unique in that they contain no carbon-carbon bonds. Nearly all otherknown organic polymers contain at least one or more carbon-carbon bondsin a portion of the recurring structural unit. Compounds which contain acarbon-carbon linkage generally carbonize and result in tracking. Sincecarbon-carbon linkage is absent from the polymers of this invention theydo not carbonize or track and are particularly well suited for use asarcand track-resistant resinous materials.

Under the influence of an electric arc, formaldehyde present in thepolymer decomposes to form carbon monoxide gas and hydrogen gas. duringarcing is particularly desirable since hydrogen assists materially inquenching and extinguishing the electric are due to its high dilfusivityand consequent rapid deionization as the alternating current approacheszero value. and the arc is extinguished at the following current zero.

Evolution of hydrogen gas Thus the arc space rapidly loses itsconductivity Because of the above properties and characteristics, highmolecular polyoxymethylene compounds are particularly suitable for usein arcand track-resistant molding compounds as well as various rubbercompounds. The polymers are particularly suitable for use in forming theinsert and tube in expulsion type lighting arresters wherein not onlyarc-expulsion and quenching is necessary but also where arc-resistanceis required.

, High molecular weight polyoxymethylene polymers also are particularlysuitable for use in forming arc-resistant and arc-expulsion apparatusbecause, unlike hard vulcanized fiber, the polymers can readily bemolded by conventional injection molding procedures into intricate andcomplex shapes. On the other hand, hard vulcanized fiber must bemachined and otherwise mechanically fabricated into its desired shape.Unlike hard vulcanized fiber, the high molecular weight polymers of thepresent invention exhibit excellent dimensional stability as a functionof humidity. Thus, the polymers absorb very little moisture.

Referring to FIG. 1 of the drawings, there is illustrated oneapplication of a high molecular weight polyoxymethylene to aself-generating gas blast circuit interrupter. Specifically, there isillustrated a fuse 10 comprising a strain wire 12 and fusible wire 14,both being connected to an upper terminal 16 which may be connected toone portion of a circuit passing through the fuse and a lower terminal18 connected by a flexible conductor 20 to a second terminal 22 which isconnectible to the complete circuit. A tube 24 surrounding the strainand fuse wires 12 and 14, respectively, is pre' pared from a highmolecular weight polyoxymethylene. If desired, only the inner portion ofthe tube 24 need be composed of high molecular weight polyoxymethylene,and the outer portion may be composed of fiber, paper, or other suitablematerial. When a suificiently high current passes through the wires 12and 14, they will fuse and thereby create an arc. The lower terminal 18will drop, either because of the gas-pressure developed by the heat ofthe are alone, or, in some cases, by a spring (not shown) operatingthereon to draw the are out further. The heat of the arc will cause thehigh molecular weight polyoxymethylene in the tube 24 to evolve gaseswhich will cause extinction of the are. It is believed that the gasesproduced by the action of the are on the polyoxymethylene are carbonmonoxide and hydrogen. The turbulent flow of these gases through thecore of the are rapidly cools and deionizes the arc whereby when thecurrent reaches zero at the end of a half cycle the arc will beextinguished Without reforming.

Referring to FIG. 3 of the drawing, there are plotted curves of restoredkilovolts against amperes, showing the interrupting ability of highmolecular weight polyoxymethylene in a one-fourth inch by four-inch borefuse. For comparative purposes, curves for fiber and boric acid derivedfrom similar fuses are shown in the graph. The curves show interruptionin five half cycles or less for each of the materials. It will be notedthat for from 45 amperes to approximately 500 amperes, high molecularweight polyoxymethylene was equal to or superior in its ability tointerrupt a higher voltage than fiber.

High molecular weight polyoxymethylenes may be used in many applicationswhere boric acid is not suitable. Specifically, since thepolyoxymethylenes have superior mechanical and chemical properties,moldability and ease of manufacture they are more suitable and indeedare preferable for use instead of boric acid.

High molecular weight polyoxymethylene polymers are particularlysuitable materials for circuit interrupters because they arenonhygroscopic and do not warp. Also, they possess extremely goodelectrical insulating properties and are insoluble in water. Thepolymers possess outstanding mechanical properties and therefore willwithstand the pressures developed by the generated gas on exposure toarcs, particularly in confined chambers.

One particularly desirable use for high molecular weightpolyoxymethylene is in self-expulsion type lightning arresters, one formof which is shown in FIG. 2 of the drawing. The lightning arrester 30comprises an exterior casing 32 preferably of porcelain to which isaffixed an external contact member 34 which is connected to a power lineor the like to be protected against lightning. An external gap isarranged between an arcing tip 36 and a cap 38 aflixcd to one end of thecasing 32. The cap 38 extends inside of the casing 32, and terminates inan arcing contact 46) disposed inside of a sleeve 42 composed of highmolecular weight polyoxymethylene. At the lower end of the sleeve 42,there is located, in threaded engagement therewith, a hollow contact 44forming an internal gap with respect to the arcing contact 40 betweenwhich an arc is adapted to be drawn upon a lightning surge passing tothe arrester 30. The hollow contact 44 is adapted to be grounded throughthe terminal 48. A slot 46 through the contact permits the expulsion ofgases through the hollow contact 44 from the interior of the sleeve 42.The distance and arrangement of the external gap 36-38 in series withthe gap between contacts 40 and 44 is predetermined and requires a surgeof a given value to be present at 34 before the lightning arrester willoperate. When a lightning surge of this given value or greater isimposed on the contact 34, an arc will pass through the gap 36-38 andinternally between contacts 4th and 44. The internal arc will cause thehigh molecular Weight polyoxymethylene sleeve =42 to produce a volume ofgas and the deionizing effect of the gas, in conjunction with thegas-blast effect, will tend to blow the are out and thereafter restorethe electrical resistance of the lightning arrester proper. The gasesproduced during the arc interrupting operation will be expelled throughthe slot 46 to the exterior of the arrester.

High molecular weight polyoxymethylenes also may be used in place offibre in oil circuit breakers as illustrated in FIG. 4. The grids 50 insuch circuit breakers can be molded as a single piece from thepolyoxymethylenes instead of assembling a plurality of stampings bybolting or the like.

While the present invention has been described with respect to what isat present, considered to be preferred embodiments thereof, it will beunderstood, of course, that certain substitutions, modifications,changes, and the like may be made therein Without departing from itstrue scope.

We claim as our invention:

1. An electric circuit interrupter comprising, in combination, conductormeans between which an arc is formed, and arc-confining andextinguishing means disposed along the path of the are from which anarc-extinguishing gas can be evolved by the heat of the arc, thearcconfining and extinguishing means comprising a body com. posedessentially of a high molecular weight polyoxymethylene.

2. An electric circuit interrupter comprising, in combination, a pair ofcontact members disposed to produce an arc to interrupt a circuitestablished between them, a chamber within which the contact members arearranged, and arc-confining and extinguishing means disposed along thepath of the arc from which an arc-extinguishing gas can be evolved bythe heat of an arc, the arc-confining and extinguishing means comprisinga body composed essentially of a high molecular weight polyoxymethylene.

3. In a fuse device, in combination, means adapted to fuse and form anare on the occurrence of an overload in an electrical circuit embodyingthe fuse device, and an arc-confining and extinguishing means disposedalong the path of the arc from which an arc-extinguishing gas can beevolved by the heat of an arc, the arc confining and extinguishing meanscomprising a body composed essentially of a high molecular weightpolyoxymethylene.

4. In a lightning arrester, in combination, means adapted to form an arewhen an electrical circuit embodying the arrester is struck bylightning, and an arc-confining and extinguishing means disposed alongthe path of the are from which an arc-extinguishing gas can be evolvedby the heat of an arc, the arc-confining and extinguishing meanscomprising a body composed essentially of a high molecular weightpolyoxymethylene.

5. An oil-type circuit interrupter including contact means forestablishing an are, a grid molded of a body composed essentially of ahigh molecular weight polyoxymethylene, and the are being extinguishedwithin said grid by evolution of gas.

References Cited in the file of this patent UNITED STATES PATENTS Stromet a1. July 18, 1950 Jones Oct. 23, 1956 MacDonald Oct. 30, 1956Sterling Sept. 10, 1957 Swerlick et a1 Sept. 20, 1960

1. AN ELECTRIC CIRCUIT INTERRUPTER COMPRISING, IN COMBINATION, CONDUCTOR MEANS BETWEEN WHICH AN ARC IS FORMED, AND ARC-CONFINING AND EXTINGUISHING MEANS DISPOSED ALONG THE PATH OF THE ARC FROM WHICH AN ARC-EXTINGUISHING GAS CAN BE EVOLVED BY THE HEAT OF THE ARC, THE ARCCONFINING AND EXTINGUISHING MEANS COMPRISING A BODY COM-- 